Articulated head with multiple sensors for measuring machine

ABSTRACT

An articulated sensor head includes three different sensor modules. A first of the sensor modules is carried on an extended shank that is mounted in a pivotable fashion from an articulating wrist. A housing carrying a second and a third of the sensor modules is releasably fastened to the extended shank. The second and third sensor modules are carried by the housing in a fixed angular orientation with respect to an orientation of the first sensor module.

TECHNICAL FIELD

The invention relates to articulated sensor heads and sensor measuringsystems of coordinate measuring machines.

BACKGROUND OF THE INVENTION

Articulated sensor heads provide for varying the orientation of sensors,particularly probes, for accessing features in different forms andorientations on workpieces or other test objects. While coordinatemeasuring machines typically include multiple axes for relatively movinga probe or other form of sensor with respect to a test object undermeasurement, articulated sensor heads generally provide one or morerotational axes that can quickly and efficiently adjust the orientationof probes or other sensor types for accommodating different features andtheir orientations on test objects.

Differently configured probes and other sensors having different sizes,sensitivities, or types of data acquisition are often needed to moreprecisely or comprehensively measure test objects with different typesand arrangements of surfaces. As such, articulated sensor heads areoften adapted to use interchangeable probes or other sensors. Inaddition to the possibility for manually exchanging probes or othersensors, automated exchange systems store the alternative probes orother sensors in docking stations and the sensor heads can be moved outof their measuring positions to and from the docking stations toexchange probes or sensors when needed. However, even the automatedexchange systems consume valuable measurement time not only through themechanical acts required to exchange the probes or other sensors butalso in one or more of repositioning, reorienting, and recalibrating thereplacement probes or other sensors for continuing measurementoperations within a common frame of reference. Issues of timeconsumption and measurement continuity are particularly problematicduring exchanges of different sensor types.

SUMMARY OF THE INVENTION

The invention in one or more of its preferred embodiments envisions amore versatile, efficient, and accurate measuring machine made possibleby an articulated sensor head arranged for carrying a range of differentsensor types in a fixed relative orientation. For example, thearticulated sensor head can be arranged to carry a touch probe, togetherwith a depth-sensing laser and a vision sensor having measurement axesin a common angular orientation with respect to each other and in apredetermined angular relationship with a measurement axis of the touchprobe.

One embodiment of the invention is based on an articulated sensor headhaving a first sensor module carried on an extended shank that ismounted in a pivotable fashion from an articulating wrist. A housingcarrying second and third sensor modules is fastened to the extendedshank. The second and third sensor modules are carried by the housing ina fixed angular orientation with respect to an orientation of the firstsensor module.

Preferably, the first, second, and third sensor modules are arranged forcollecting information about test objects in different ways. Forexample, the first sensor module can be part of a touch probe thatcollects information from relative physical displacements of a styluswith respect to the test object, the second sensor module can be part ofa depth-sensing laser that collects information from laser beamreflections from the test object, and the third sensor module can bepart of a vision sensor that collects information from camera imagestaken of the test object. The vision sensor preferably includes aco-axial light source.

Preferably, each of the three sensor modules has a reference measurementposition that is calibrated with respect to the reference measurementpositions of the other sensor modules by displacements of thearticulated sensor head. Thus, the same location on the test object canbe measured by each of the three sensor modules by the calibrateddisplacements of the articulated sensor head. In this regard, each ofthe three sensor modules includes a measurement axis, and themeasurement axes of the second and third sensor modules preferably sharea common fixed angular orientation in a predetermined angularrelationship with the measurement axis of the first sensor module. Morepreferably, the measurement axes of all three sensor modules extend inparallel.

To provide further flexibility for measuring different test objects indifferent ways, the first sensor module is preferably interchangeablewith other sensor modules. For example, a first coupling can be providedbetween the first sensor module and the extended shank, thereby allowingthe first sensor module to be exchanged with alternative sensor modulesindependently of the second and third sensor modules carried in thehousing, which is separately attached to the extended shank. One memberof the first coupling can be mounted on a free end of the shank, and amating coupling member can be mounted on the first sensor module and oneach of the alternative sensor modules intended to be independentlycoupled to the shank. The second and third sensor modules can becollectively attached or detached from the shank by attaching thehousing to an intermediate portion of the extended shank using aremovable clamp or other releasable fastening device including couplingsthat are located along the extended shank or between the extended shankand the housing. Once the housing is detached, measurements can be takenby the first sensor module alone or a similarly attachable alternativehousing carrying one or more different sensor modules can be clamped orotherwise releasably fastened to the intermediate portion of theextended shank for taking additional measurements. A similar couplingwithin the housing can be arranged to allow the second sensor module tobe replaced by a similarly coupleable alternative sensor moduleindependently of the first and third sensor modules. Docking stationscan be provided for holding the alternative sensor modules for replacingthe first and second sensor modules as well as the alternative housingcarrying alternative second or third sensor modules.

An embodiment of the invention as a method of measuring a test objectwith an articulated sensor head includes measuring a given point on atest object with a first of three sensor modules each having a referencemeasurement position that is calibrated with respect to the referencemeasurement positions of the other sensor modules by displacements ofthe articulated sensor head. The articulated sensor head is displaced bythe displacement calibrated between the reference measurement positionsof the first sensor module and a second of the three sensor modules. Thegiven point on the test object is measured with the second sensor moduleat the displaced position of the articulated sensor head.

The articulated sensor head can be further displaced by the displacementcalibrated between the reference measurement positions of the secondsensor module and a third of the three sensor modules. The given pointon the test object can be measured with the third sensor module at thefurther displaced position of the articulated sensor head. Preferably,the calibrated displacements of the articulated sensor head are carriedout by translations of the articulated sensor head.

The measurement method also preferably includes releasably coupling thefirst of the three sensor modules to an extended shank of thearticulated sensor head and releasably coupling a housing carrying thesecond and third sensor modules to the extended shank. For takingadditional measurements, the first sensor module can be replaced with adifferent sensor module by decoupling the first sensor module from theextended shank and coupling the different sensor module to the extendedshank using a portion of a first sensor module coupling that remains onthe extended shank. Similarly, the housing carrying the second and thirdsensor modules can be replaced with a different housing carrying atleast one different sensor module by decoupling the housing from theextended shank and coupling the different housing to the extended shankusing a portion of a housing coupling that remains on the extendedshank.

The third sensor module can be a vision sensor having a variable workingdistance lens and an adjustable co-axial light source for illuminatingthe test object at different working distances. As such, the measurementmethod can include adjusting the working distance of the lens togetherwith adjusting the co-axial light source for illuminating the testobject at the adjusted working distance of the lens.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a perspective view of an articulated sensor head in accordancewith an embodiment of the invention.

FIG. 2 is a front view of the articulated sensor head of FIG. 1.

FIG. 3 is a side view of the articulated sensor head of FIG. 1.

FIG. 4 is another perspective view of the articulated sensor head ofFIG. 1 in a fully pivoted position about a pivot axis.

FIG. 5 is a substantially front perspective view of the articulatedsensor head of FIG. 1 captured as an image.

FIG. 6 is a another perspective view of the same articulated sensorhead.

FIG. 7 is a side view of a similar articulated sensor head featuring acoupling along an extended shank for releasably attaching a housingcarrying sensor modules to the extended shank.

FIG. 8 is a side view of a similar articulated sensor head featuring acoupling located between the extended shank and the housing forreleasably attaching the housing carrying sensor modules to the extendedshank.

FIG. 9 is a side view of a vision sensor of a type that can be carriedin the housing including a broken out section showing a variable focallength lens.

DETAILED DESCRIPTION OF THE INVENTION

A featured embodiment of an articulated sensor head 10 as shown in thedrawing figures includes a first sensor module 12 in the form of a touchprobe stylus carried on an extended shank 14. An articulating wrist 16,which can be supported from a measurement axis of a coordinate measuringmachine, connects one end of the extended shank 14 to a pivot axis 18.The depicted articulating wrist 16 preferably includes a motorizedassembly for pivoting the shank 14 about the pivot axis 18 through alimited range of angular travel as referenced between differentorientations of the shank 14 shown in FIGS. 1 and 4. A second motorizedassembly of the articulating wrist can be provided for rotating theshank 14 about a vertical axis aligned with the extended shank 14 in thearticulated position shown in FIGS. 1-3. The coordinate measuringmachine can provide additional relative translational and rotationalmotions of the articulated sensor head 10 with respect to a test object30 by moving one or both of the articulated sensor head 10 and the testobject 30. The articulating wrist 16 and extended shank 14 can befashioned as a Renishaw PH10MQ motorized probe head from Renishaw Inc.of 5277 Trillium Blvd., Hoffman Estates, Ill. 60192.

A housing 20, which is attached to the extended shank 14 carries both asecond sensor module 22 in the form of a depth-sensing laser and a thirdsensor module 24 in the form of a vision sensor. The housing 20 is shownin at least FIGS. 1-6 attached to the shank 14 by a removable clamp 26.The second sensor module 22 as a depth-sensing laser can be compactinterferometer laser sensor using a narrow range of beam frequencies tomeasure distances to the test object based on the rate ofinterferometric phase variations with beam frequency. The third sensormodule 24 as a vision sensor can include a Basler acA2500-14 gm, 5-MPdigital camera with a multi-sector, green LED ring light 28 and abandpass filter (500-550 nm) in front of the camera to reduce thesensitivity of the camera to ambient light. The referenced camera isavailable from Basler, Inc., Exton, 855 Springdale Drive, Suite 203,Exton, Pa. 19341.

Each of the sensor modules includes a measurement axis, whichcontributes to defining a central measurement position along themeasurement axis of each sensor, i.e., as a measurement positionrecognized as lying within a common coordinate system. The first sensormodule 12 as a touch probe stylus 12 has a measurement axis 32 thatextends through the probe tip. The second sensor module 22 as adepth-sensing laser has a measurement axis 34 that extends along anoptical axis of its emitted laser beam. The third sensor module 24 as avision sensor has a measurement axis 36 that extends along an opticalaxis of its objective imaging optics. The ring light 28 is positionedco-axial with the measurement axis 36.

The second sensor module 22 and the third sensor module 24 are mountedwithin the housing 20 so that their measurement axes 34 and 36 aremaintained in a fixed angular orientation with respect to themeasurement axis 32 of the first sensor module 12 throughout the rangeof articulation about the pivot axis 18 of the articulating wrist 16.Preferably, the fixed angular orientation of the measurement axes 34 and36 is held within 20 degrees of the measurement axis 32. More preferablyas shown, the measurement axes 32, 34, and 36 all extend in parallel.The fixed offset relationships among the measurement axes 32, 34, and 36including their respective measurement positions along their measurementaxes can be calibrated with displacements of the articulated sensor head10 so that the same point on the test object 30 can be quickly measuredby any one of the three sensor modules. The required displacements ofthe articulated sensor head 10 can be effected by one or more motionaxes of the coordinate measuring machine or another motion axis throughthe articulated sensor head while accounting for any angulardisplacements of the articulated sensor head 10. Thus, the same locationon the test object 30 can be readily measured by each of the threesensor modules, which provide different types of measurements withoutrequiring any of the sensor modules to be replaced or moved out ofproximity with the test object 30.

To provide additional flexibility for measuring test objects indifferent ways, the first sensor module is preferably interchangeablewith alternative sensor modules. For example, a first coupling 40 havinga coupling member 42 attached to the free end of the shank 14 and amating coupling member 44 attached the first sensor module 12 allows thefirst sensor module 12 to be exchanged with alternative sensor moduleshaving a similar mating coupling member independently of the second andthird sensor modules. The alternative sensor modules, which can bedifferent touch probe styluses or sensor modules for carrying outdifferent types of measurements, can be stored in a docking station thatis within the travel range of the coordinate measurement machine forcarrying out automated exchanges in a known manner.

The second and third sensor modules can be collectively attached ordetached from the extended shank 14 via the removable clamp 26, whichcan be clamped to an intermediate portion of the extended shank 14 bytightening the clamp 26 or released from the intermediate portion of theshank 14 by loosening the clamp 26. Once the housing 20 is detached,measurements can be taken by the first sensor module 12 without carryingthe weight or bulk of the housing 20. Alternatively, another housingcarrying one or more different sensor modules can be clamped orotherwise releasably fastened to the shank for taking additionalmeasurements. In an alternative housing, the second sensor module 22 canbe another depth-sensing laser further adapted to a desired measurementand a third sensor module 24 can be another a vision sensor furtheradapted to a desired measurement, or either or both of the second andthird sensor modules can be arranged for taking different types ofmeasurements.

A similar coupling 48 within the housing 20 can be arranged to allow thesecond sensor module 22 to be replaced by a similarly coupleablealternative sensor module independently of the first and third sensormodules. A docking station within the range of travel of the coordinatemeasuring machine can be arranged to hold one or more alternative secondsensor modules to support the automated exchange of the second sensormodules. One or more alternative housings can also be stored in adocking station positioned for convenient replacement of the housing 20.In a manner similar to the first coupling 40, the coupling 48 caninclude a coupling member attached to the housing and a mating couplingmember attached second sensor module 22. Alternative sensor moduleshaving a similar mating coupling member can be exchanged with the secondsensor module independently of the first and third sensor modules.

To allow a full range or at least a desired range of motion about thepivot axis 18, the housing 20 is preferably attached along theintermediate portion of the extended shank 14 at a displacement D fromthe pivot axis 18 that avoids interference between the housing 20 andthe articulating wrist 16 or its connection to the coordinate measuringmachine. For example, with respect to the referenced Renishaw PH10MQmotorized probe head, the housing is preferably clamped at a distance ofapproximately 65 mm or more from the probe axis 18.

For measuring the test object 30 with the articulated sensor head 10,reference measurement positions of each of the three sensor modules 12,22, and 24 are calibrated with respect to each other as relativedisplacements of the articulated sensor head 10. A first measurement istaken of a given point on the test object 30 with a first of the threesensor modules 12, 22, and 24. The given point can be one of a pluralityof points captured by the first-referenced sensor module. For taking asecond measurement of the test object 30 with a second of the threesensor modules 12, 22, and 24 at the given point on the test object 30,the articulated sensor head 10 is displaced by the calibrated amount ofdisplacement between the reference measurement positions between thefirst-referenced and second-referenced sensor modules. For taking athird measurement of the test object 30 with a third of the three sensormodules 12, 22, and 24 at the given point on the test object 30, thearticulated sensor head 10 is displaced by the calibrated amount ofdisplacement between the reference measurement positions of thesecond-referenced and third-referenced sensor modules. By arranging therespective measurement axes 32, 34, and 36 of the three sensor modules12, 22, and 24 in parallel, the calibrated displacements can besimplified and carried out by translations of the articulated sensorhead 10. The referenced measurement positions can be calibrated bymeasuring a common test feature in a given orientation with each of thethree sensor modules and recording the relative displacements betweenthe sensor modules required for the collective points measured by thesensor modules to correspond within a common coordinate system withinnotable ranges of tolerances associated with the repeatability of themeasurements.

FIGS. 7 and 8 feature alternative ways of attaching the housing 20carrying the second and third sensor modules 22 and 24 to the extendedshank 14. In FIG. 7, the housing 20 is fixed (e.g., clamped) to anintermediate section 54 of the extended shank 14. For example, the clamp26 can be either removable or permanently fixed to the intermediatesection 54 of the extended shank 14 for purposes of convenience beyondthe need for replacing the housing 20 with another housing. Instead, theintermediate section 54 of the extended shank 14 is coupled to an uppersection 52 of the extended shank 14 through a coupling 60 and is coupledto a lower section 56 of the extended shank through the coupling 40. Theupper section 52 of the extended shank 14 is connected to thearticulating wrist 16, and the lower section 56 of the extended shank ispart of the first sensor module 12. The coupling 60, which is similar tothe coupling 40, includes a coupling member 62 attached to the uppersection 52 of the extended shank 14 and a mating coupling member 64attached intermediate section 54 of the extended shank 14. Whiledecoupling the coupling 60 detaches both the first sensor module 12 andthe housing 30 carrying the second and third sensor modules 22 and 24from the upper section 52 of the extended shank 14, the housing 20 canbe replaced by a different housing carrying different second or thirdsensor modules fixed to a similar intermediate section without replacingthe first sensor module 12. That is, the replacement intermediatesection with the different fixed housing can be coupled to the uppersection 52 of the extended shaft 14, and the original lower section 56of the extended shaft 14 as a part of the first sensor module 12 can becoupled to the replacement intermediate section. To allow for the firstsensor module 12 to be operated without the weight and bulk of thehousing 20 carrying the second and third sensor modules 22 and 24, areplacement intermediate section can be provided, which is not fixed tosuch a housing.

In FIG. 8, the housing 20 is coupled to the intermediate portion of theextended shank 14 through a coupling 70 located between the housing 20and the clamp 26. Once again, the clamp 26 can be either removable orpermanently fixed to the intermediate portion of the extended shank 14for purposes of convenience beyond the need for replacing the housing 20with another housing. The coupling 70, which can also be similar to thecoupling 40, includes a coupling member 72 attached to the clamp 26 anda mating coupling member 74 attached to the housing 20. The housing 20together with the second and third sensor modules 22 and 24 can beattached or detached from the extended shank 14 via the coupling 70. Onecoupling member 72 of the coupling 70 is attached to the clamp 26 and amating coupling member 74 is attached to the housing 20. Once thehousing 20 is detached, measurements can be taken by the first sensormodule 12 without carrying the weight or bulk of the housing 20.Alternatively, another housing carrying one or more different sensormodules and having a similar mating coupling member can be coupled tothe extended shank 14 through the coupling member 72 attached to theclamp 26 for taking additional measurements.

Preferably, the couplings 40, 48, 60, and 70 are kinematic couplingswhereby the individual sensor modules or housings can be coupled andrecoupled while maintaining precision and certainty of location tominimize requirements for recalibration. The light sources used with thevision sensors can be arranged to provide the type of lighting requiredfor the desired vision measurement including directing light withindesired wavelength bands over desired ranges of incidence angles andappropriately sized areas at the desired working distance.

The third sensor module 24 as a part of a vision sensor is depicted inFIG. 9 with a variable focal length lens 80 for adjusting a workingdistance between an end face 82 of the sensor module 24 and the focalplane of the variable focal length lens 80. For example, a first workingdistance W1 is depicted for one focal length and a second workingdistance W2 is depicted for a second focal distance. While variablefocal length lenses can be constructed in a variety of known ways, thevariable focal length lens 80 is depicted with electrodes 84 whosevoltages can be controlled to change the shape of an electro-reactivefluid filled lens.

To accommodate the variable working distances, e.g., W1 and W2, effectedby the variable focal length lens 80, the third sensor module 24 canalso include an adjustable light source 90, which can be adjusted tomaintain desired ranges of incidence angles and appropriately sizedareas at the desired working distance. The adjustable light source 90can be adjusted by a linear actuator depicted as the arrow 92 totranslate the light source 90 along the measurement axis 36 inaccordance with the changes in working distance along the same axis.Alternatively, the angular orientations of light beams emitted by thelight source can be angularly adjusted with respect to the measurementaxis to illuminate the desired area on a test part at the differentworking distances. Variable lighting patterns at different transversediameters or aperture sizes could also be used.

While the above description references certain embodiments in detail, itwill be understood that variants of these embodiments and other featuresand functions and alternatives thereof may be combined into may otherdifferent systems or applications. As such, various presently unforeseenor unanticipated alternatives, modifications, variations or improvementstherein may be subsequently made by those skilled in the art, which arealso intended to be encompassed by the following claims.

1.-13. (canceled)
 14. An articulated sensor head comprising: a firstsensor module carried on an extended shank that is mounted in apivotable fashion from an articulating wrist; a housing carrying secondand third sensor modules fastened to the extended shank; and the secondand third sensor modules being carried by the housing in a fixed angularorientation with respect to an orientation of the first sensor module,wherein the third sensor module is a part of a vision sensor thatcollects information from camera images taken of the test object, andthe vision sensor includes an electro-reactive fluid filled lens havinga variable working distance along a measurement axis.
 15. Thearticulated sensor head of claim 14 in which the vision sensor includesa light source that is coaxial with the measurement axis and isadjustable for illuminating a test object at variable working distances.16.-22. (canceled)
 23. The articulated sensor head of claim 15 in whichthe light source is adjustable along the measurement axis.
 24. Thearticulated sensor head of claim 14 in which the second and third sensormodules are collectively attachable and detachable from the extendedshank independently of the first sensor module.
 25. The articulatedsensor head of claim 24 further comprising a first coupling forreleasably connecting the first sensor module to the extended shank sothat the first sensor module is exchangeable with a similarly coupleablealternative sensor module independently of the second and third sensormodules.
 26. The articulated sensor head of claim 25 further comprisinga second coupling for releasably connecting the housing carrying thesecond and third sensor modules to the extended shank so that thehousing is interchangeable with a similarly coupleable alternativehousing without disconnecting the first sensor module from the extendedshank.
 27. The articulated sensor head of claim 14 in which the extendedshank includes a length with a first releasable coupling along a firstportion of the length of the extended shank and a second releasablecoupling along a second portion of the length of the extended shank, andin which the housing carrying the second and third sensor modules isfixed to a third portion of the length of the extended shank between thefirst and second portions of the extended shank.
 28. The articulatedsensor head of claim 27 in which the first releasable coupling providesfor releasably connecting the first sensor module to a free end of theextended shank.
 29. The articulated sensor head of claim 14 in whicheach of the three sensor modules includes a measurement axis, themeasurement axis associated with the working distance ofelectro-reactive fluid filled lens corresponds to the measurement axisof the third sensor module, and the measurement axes of the second andthird sensor modules share a common fixed angular orientation in apredetermined angular relationship with the measurement axis of thefirst sensor module.